<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width,initial-scale=1.0,user-scalable=no">
    <title>Title</title>
    <style>
        * {
            margin: 0;
            padding: 0;
        }
        body {
            height: 100vh;
            overflow: hidden;
        }
    </style>
</head>
<body>

</body>
<script>
    var canvas  = document.getElementById("demo");
    if (canvas.getContext){
        var ctx = canvas.getContext("2d");
    }
</script>
</html>